There is no NULL value in EdgeDB unlike in many other
databases or programming languages. This is deliberate,
as NULL scalars create all sorts of problems when interacting with other data and operations.
Instead of the NULL scalar value EdgeDB uses an empty
set {} to denote the absence of data. The advantage
of using the empty set is that it works exactly like
every other set in every way. Its behavior is
well-defined and consistent across all operators and
functions.
For example, "count" will give the number of elements in an empty set:
The EXISTS operator returns false if the set is
empty and true otherwise:
Usually it is necessary to provide the type of the empty
set using a cast, when the type is relevant and cannot
be assumed (like in INSERT queries):
When an empty set is used as an element-wise operand or element-wise parameter of a function, the result is always an empty set, too (albeit of whatever the return type is). This is because the Cartesian product of the empty set with anything else is still an empty set:
Because of its ability of making any Cartesian product into another empty set, there are some gotchas when an empty set is used where an array or tuple element are expected:
Typically, if you want to splice 0 or 1 elements into an
array the "array_agg" function and concatenation should
be used. Try the following example with different values
specified for x:
